Outage Analysis and Location Estimation of Cooperative GEO/LEO ISAC Network with Imperfect CSI

Abstract As the demand for integrated connectivity and wide-area sensing in sixthgeneration (6G) non-terrestrial networks, satellite integrated sensing and communication (SAT-ISAC) has attracted increasing attention in recent works. However, due to the limited echo signal power in monostatic GEO satellite ISAC systems, bistatic GEO/LEO satellite ISAC offers enhanced echo signal strength and cooperative communication capabilities, making it a promising research direction. This paper investigates the cooperative target sensing and multi-user communication of a two-layer satellite system with the consideration of imperfect channel state information (CSI). First, we analyze the detection probability of sensing signal and the outage probability (OP) of terrestrial user terminals (UTs). Besides, the asymptotic OP is derived to characterize the communication performance in the high signal-to-noise ratio (SNR) region. To enhance sensing performance, a statistical detection probability maximization problem is proposed, while ensuring OP constraint, a successive convex approximation (SCA) based beamforming design strategy is proposed . Additionally, the target location estimation is introduced, leveraging the advantages of cooperative GEO/LEO network to estimate the delay and angle information. The Crame´r-Rao Bound (CRB) is also derived as a low bound on the mean square error of the parameter estimates. Finally, we validate the theoretical findings through Monte Carlo simulations, which demonstrate that the proposed beamforming algorithm can effectively support target sensing tasks. The optimization results show that the proposed algorithm achieves superior performance.